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From: Jeff King <peff@peff.net>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: git@vger.kernel.org, Martin Ågren <martin.agren@gmail.com>,
	Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 3/5] match-trees: use hashcpy to splice trees
Date: Thu, 10 Jan 2019 01:45:20 -0500
Message-ID: <20190110064520.GC20497@sigill.intra.peff.net> (raw)
In-Reply-To: <20190110042551.915769-4-sandals@crustytoothpaste.net>

On Thu, Jan 10, 2019 at 04:25:49AM +0000, brian m. carlson wrote:

> When we're splicing trees, we're writing directly from one location into
> a buffer that is exactly the same size as a tree object. If the current
> hash algorithm is SHA-1, we may not have a full 32 (GIT_MAX_RAWSZ) bytes
> available to write, nor would we want to write that many bytes even if
> we did. In a future commit, we'll split out hashcpy to respect
> the_hash_algo while oidcpy uses GIT_MAX_RAWSZ, so convert the oidcpy to
> a hashcpy so we copy the right number of bytes.
> 
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
>  match-trees.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/match-trees.c b/match-trees.c
> index feca48a5fd..b1fbd022d1 100644
> --- a/match-trees.c
> +++ b/match-trees.c
> @@ -224,7 +224,7 @@ static int splice_tree(const struct object_id *oid1, const char *prefix,
>  	} else {
>  		rewrite_with = oid2;
>  	}
> -	oidcpy(rewrite_here, rewrite_with);
> +	hashcpy(rewrite_here->hash, rewrite_with->hash);

Hrm. Our coccinelle patches will want to convert this back to oidcpy(),
though I see you drop them in the final patch.

However, I wonder if it points to another mismatch. Isn't the point that
we _don't_ actually have "struct object_id"s here? I.e., rewrite_here
and rewrite_with should actually be "const unsigned char *" that we
happen to know are the_hash_algo->raw_sz?

I think the only reason they are "struct object_id" is because that's
what tree_entry_extract() returns. Should we be providing another
function to allow more byte-oriented access?

-Peff

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-07 23:34 What's cooking in git.git (Jan 2019, #01; Mon, 7) Junio C Hamano
2019-01-08  9:50 ` tg/checkout-no-overlay, was " Thomas Gummerer
2019-01-08 17:51   ` Junio C Hamano
2019-01-08 17:30 ` ag/sequencer-reduce-rewriting-todo " Alban Gruin
2019-01-08 21:20 ` sb/more-repo-in-api, was " Jonathan Tan
2019-01-08 21:35   ` Junio C Hamano
2019-01-09 21:28     ` Stefan Beller
2019-01-09  7:37 ` Martin Ågren
2019-01-09 21:06   ` Martin Ågren
2019-01-10  1:02     ` brian m. carlson
2019-01-10 18:55       ` Junio C Hamano
2019-01-10 19:03       ` Martin Ågren
2019-01-10  4:25     ` [PATCH 0/5] tree-walk object_id refactor brian m. carlson
2019-01-10  4:25       ` [PATCH 1/5] tree-walk: copy object ID before use brian m. carlson
2019-01-10  4:25       ` [PATCH 2/5] match-trees: compute buffer offset correctly when splicing brian m. carlson
2019-01-10  4:25       ` [PATCH 3/5] match-trees: use hashcpy to splice trees brian m. carlson
2019-01-10  6:45         ` Jeff King [this message]
2019-01-10 23:55           ` brian m. carlson
2019-01-11 14:51             ` Jeff King
2019-01-11 14:54               ` Jeff King
2019-01-14  1:30                 ` brian m. carlson
2019-01-14 15:40                   ` Jeff King
2019-01-10  4:25       ` [PATCH 4/5] tree-walk: store object_id in a separate member brian m. carlson
2019-01-10  6:49         ` Jeff King
2019-01-10 23:57           ` brian m. carlson
2019-01-10  4:25       ` [PATCH 5/5] cache: make oidcpy always copy GIT_MAX_RAWSZ bytes brian m. carlson
2019-01-10  6:50         ` Jeff King
2019-01-10  6:40       ` [PATCH 0/5] tree-walk object_id refactor Jeff King
2019-01-11  0:17         ` brian m. carlson
2019-01-11 14:17           ` Jeff King
2019-01-15  0:39     ` [PATCH v2 " brian m. carlson
2019-01-15  0:39       ` [PATCH v2 1/5] tree-walk: copy object ID before use brian m. carlson
2019-01-15  0:39       ` [PATCH v2 2/5] match-trees: compute buffer offset correctly when splicing brian m. carlson
2019-01-15  0:39       ` [PATCH v2 3/5] match-trees: use hashcpy to splice trees brian m. carlson
2019-01-15  0:39       ` [PATCH v2 4/5] tree-walk: store object_id in a separate member brian m. carlson
2019-01-15  0:39       ` [PATCH v2 5/5] cache: make oidcpy always copy GIT_MAX_RAWSZ bytes brian m. carlson
2019-01-15 17:51       ` [PATCH v2 0/5] tree-walk object_id refactor Junio C Hamano
2019-01-09 10:28 ` What's cooking in git.git (Jan 2019, #01; Mon, 7) Jeff King
2019-01-10 19:05   ` Junio C Hamano
2019-01-10 19:46   ` Junio C Hamano
2019-01-10 18:02 ` Stefan Beller

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